1. Field of the Invention
The present invention relates to industrial fabrics. More particularly, the invention relates to a multi-pin seam for a woven fabric wherein the weave pattern in the seam area more closely conforms to that in the weave pattern in the fabric body.
2. Description of the Related Art
The production of nonwoven fabrics is well known in the art. Such fabrics are produced directly from fibers without conventional spinning, weaving or knitting operations. Instead, they may be produced by spun-bonding or melt-blowing processes in which newly extruded fibers are laid down to form a web while still in a hot, tacky condition following extrusion, whereby they adhere to one another to yield an integral nonwoven web.
Nonwoven product may also be produced by air-laying or carding operations where the web of fibers is consolidated, subsequent to deposition, into a nonwoven product by needling or hydroentanglement. In the latter, high-pressure water jets are directed vertically down onto the web to entangle the fibers with each other. In needling, the entanglement is achieved mechanically through the use of a reciprocating bed of barbed needles which force fibers on the surface of the web further thereinto during the entry stroke of the needles.
Endless industrial fabrics play a key role in these processes. Generally, these fabrics are woven from plastic monofilament, although metal wire may be used instead of plastic monofilament when, for example, temperature conditions during a nonwovens manufacturing process make it impractical or impossible to use plastic monofilament. As is the case with other industrial fabrics like paper machine clothing, such industrial fabrics also function in the manner of conveyors on which the webs are laid down and consolidated in a continuous fashion according to the methods described above.
It should be recalled that, at one time, industrial fabrics, particularly ones used in the production of nonwovens and certain aspects of papermaking, were supplied only in endless form. This is because the fibrous web being produced is extremely susceptible to defects such as marking by any nonuniformity in the fabric or fabrics. An endless, seamless fabric, such as one produced by the process known as endless weaving, has a uniform structure in both its longitudinal (machine) and transverse (cross-machine) directions. A seam, such as a seam which may be used to close the fabric into endless form during installation on a machine, represents a discontinuity in the uniform structure of the fabric. The use of a seam, then, greatly increases the likelihood that the cellulosic or synthetic fibrous web will be marked for example.
Furthermore, some industrial machine producing products such as nonwovens have solid frames. This means that either a significant portion of the machine is taken apart or dismantled or both to install an endless fabric; or what was required was to develop fabric that had seams that could be installed and made endless by closing the seam. Early prior art fabrics had seams of various types, all of which formed a noticeable discontinuity in the fabric.
Several varieties of industrial fabrics are designed to be closed into endless form during installation of production machines. For example, papermaker's dryer fabrics may be joined into the form of an endless loop during installation in a dryer section of a paper producing machine. Dryer fabrics may be so joined with a pin seam. Other industrial fabrics, such as the aforenoted fabrics for the manufacture of nonwovens, in addition to corrugator belts, pulp-forming fabrics and sludge-dewatering fabrics and DNT dewatering fabrics, are seamed in a similar fashion.
For this reason, the seam region of any workable on-machine-seamable fabric must behave as best it can, like the rest of the fabric, in order to prevent the periodic marking of the product being manufactured by the seam region of the fabric.
Despite the considerable technical obstacles presented by these requirements, it remained highly desirable to develop an improved on-machine-seamable fabric. Ultimately, these obstacles were overcome with the development of fabrics having seams formed by providing seaming loops on the crosswise edges of the two ends of the fabric. The seaming loops themselves may be formed by the machine-direction (MD) yarns of the fabric. The seam is closed by bringing the two ends of the fabric together, by interdigitating the seaming loops at the two ends of the fabric, and by directing a so-called pin, or pintle, through the passage defined by the interdigitated seaming loops to lock the two ends of the fabric together. Needless to say, it is much easier and far less time-consuming to install an on-machine-seamable fabric, than it is to install an endless fabric, on a machine.
One method to produce a fabric that can be joined on a machine with such a seam is to flat-weave the fabric. In this case, the warp yarns are the machine-direction (MD) yarns of the fabric. To form the seaming loops, the warp yarns at the ends of the fabric are turned back and woven some distance back into the fabric body in a direction parallel to the warp yarns.
In certain instances multi-pin or pintle seams may be desired. In this regard FIG. 1B (plan view), FIG. 2B, and FIGS. 3A and 3B (cross section) illustrate a prior art standard double pin seam on an asymmetrical single layer fabric 10. As seen in FIG. 1B, the fabric 10 comprises a plurality of rows of MD yarns 14 interwoven with a single layer of CD yarns 12. In the seam area, each MD yarn 14 form a seaming loop 16 around two joining pins or pintles 18. In this way, the double pin seam is used to join the two ends of the fabric 10. Each of FIGS. 3A and 3B show a cross section of this fabric 10 (the left and right fabric ends appear separated, and the two pins 18 appear twice, for clarity only) on the machine during installation. The pins are removed from the fabric ends with the loops interdigitated and the pins reinserted creating the seam and making the fabric endless. As can be seen, a first row of MD yarns 14 is formed, then a second row and so on with this sequence of first and second rows repeated over and over to form a full width fabric 10.
As illustrated in each of FIGS. 3A and 3B, the weave pattern in the fabric body (i.e., non-seam area) is such that the MD yarns 14 define long floats over the CD yarns 12 on the fabric face, and short knuckles on the back of the fabric 10. The weave pattern in the seam area, however, is different than that in the fabric body. In the seam area, the MD yarns 14 merely form loops 16 around the pins 18 at the fabric ends. This dissimilarity between the weave of the fabric body and that of the seam area results in a discontinuity on the fabric surface. This discontinuity is also shown in FIG. 2B (cross sectional view), and unfortunately, can lead to marking of a product carried on the fabric or abrasion of the seam area of the fabric by stationary elements 10 during use.
This discontinuity also exists in the case of a standard double pin seam on a symmetrical double layer fabric. FIGS. 4D and 4E show a cross section of the fabric ends joined using the two pins 18 (In FIG. 4E, the left and right fabric ends appear separated, and the two pins 18 appear twice, for clarity only). As can be seen, a first row of MD yarns 14 is formed, then a second row, and so on with this sequence of first and second rows repeated over and over to form a full width fabric 10.
As illustrated in each of FIGS. 4D and 4E, the weave in the fabric body is such that the MD yarns 14 define knuckles on both the fabric face and back. The weave pattern in the seam area, however, is different than that in the fabric body. In the seam area, the MD yarns 14 again merely form loops 16 around the pins 18 at the fabric ends. In some instances alternative rows of MD yarns 14 can form differing loop lengths and geometries resulting in dissimilarities between the seam and the body of the fabric. As mentioned above, this dissimilarity between the weave of the fabric body and that of the seam area results in a discontinuity on the fabric surface. As previously mentioned, this discontinuity can lead to marking of a product carried on the fabric or abrasion of the fabric seam itself by stationary objects.
In view of the foregoing, there exists a need for a seam having a weave pattern that conforms more closely to the weave pattern in the rest of the fabric.